Having problems with message search?
From the standpoint of an Oracle programmer/dba there is a difference between a 0 and a NULL.
A zero is a value. It's value is ZERO.
A null by definition is an ABSENCE of a value.
If you're not careful with the above distinctions you could default a value to 0 when it should actually remain a NULL and by doing so throw off statistics.
For example a table with 10 rows of values:
In the first - 5 values defaulted to 0 and 5 values with actual values. The average of the values in table is 1.5
0
0
0
0
0
1
2
3
4
5
0
0
0
0
1
2
3
4
5
In the second table - 5 values NOT defaulted to 0 and the same 5 actual values as the first. The average of the values in this table is 3.
NULL
NULL
NULL
NULL
NULL
1
2
3
4
5
NULL
NULL
NULL
NULL
1
2
3
4
5
The difference is in the first table the average function AVG() is using ALL the values even the 0 values. In the second the NULL values don't exist so the AVG() function is only using the 5 values it knows about.
Online Now 
Send Email
